The present invention pertains to exhaust systems for water craft internal combustion engines; more particularly, it pertains to improved marine wet exhaust systems for reducing the emission of particulate materials and petroleum based contaminants into the environment.
Internal combustion engines commonly used to power water craft generate power through rapid combustion of organic fuels and the resulting expansion of the combustion products against pistons coupled to drive shafts. The combustion products typically include particulates capable of polluting the surrounding air or water. The periodic combustion, expansion and discharge of the combustion products also produce undesirable heat and noise in the exhaust flow from the engine. Such internal combustion engines are also used to drive generators to produce electrical energy to supply the electrical systems on board the water craft. The marine wet exhaust system herein described is applicable to all such internal combustion engines so installed on marine water craft.
Water craft internal combustion engines typically use the water supporting the craft for cooling purposes. The water is drawn into the water craft engine, via an engine driven cooling water supply pump, and circulated through an engine cooling jacket or engine coolant heat exchanger. After circulating through the engine cooling jacket, the water is commonly injected into the exhaust system to cool the combustion products and exhaust gases for safe discharge through the hull of the craft, thereby minimizing fire hazard. Accordingly, a marine wet exhaust system must handle not only exhaust gases, but also the waste cooling water which is injected into the exhaust system.
One drawback to such systems is that the rate at which the water is drawn in by the cooling water supply pump likely differs from the rate at which water can be discharged through the marine wet exhaust system, possibly resulting in undesired pressure gradients or accumulations of water in the marine wet exhaust system.
The exhaust gases flowing out of the water separation component will have very high water content in vapor form. The gases may also contain unburned fuel in vapor form. As these gases travel downstream toward the exhaust terminus, they are cooled. The cooling is nearly always sufficient to cause condensation of both the water vapor and the fuel vapor. This process results in liquid condensates that will be included in the gas flow from what might have been expected to be a dry exhaust gas terminus.
In many installations, this can be very objectionable, particularly if the so-called dry exhaust gas outlet has been positioned over a deck or other space on board the craft where the accumulation of such liquids would be very undesirable.
In addition to safely handling exhaust gases and waste cooling water, a marine wet exhaust system should muffle or attenuate the exhaust noise generated by operation of the marine craft engine. Muffling of exhaust noise from marine engines has been handled in a number of ways. For example, the exhaust may be discharged below the water level. In outboard engines, and in inboard/outdrive installations, the exhaust is sometimes routed through the drive unit so that the exhaust gas and waste cooling water are discharged through or adjacent the propeller driving the craft. An exhaust system including a water separator for use in outboard drive units with exhaust routed through the propeller under the water line is proposed in North et al., U.S. Pat. No. 3,759,041, the disclosure of which is incorporated herein by reference.
In other systems, the wet exhaust flows through muffler/separators which remove at least a portion of the cooling water from the exhaust flow. Secondary mufflers are often placed along the exhaust conduit running between such muffler/separators and the exhaust gas line termini to further attenuate the exhaust noise. One such muffler is proposed in Harbert, U.S. Pat. No. 5,022,877, the disclosure of which is incorporated herein by reference.
Marine mufflers are generally constructed of materials such as fiberglass which can tolerate the exhaust gases and cooling water. While currently available fiberglass mufflers are popular in the boating industry, many do not provide good attenuation of the noise generated by marine engines. Furthermore, such mufflers often do not adequately separate water from the exhaust gases, even if they are designed to perform any water separation at all.
Catalytic converters have been used in land vehicles to adsorb or otherwise remove particulates from automotive internal combustion engine exhaust flows. Such devices are less practical in marine craft, however, inasmuch as the very high temperatures necessary for the reduction processes in catalytic converters cannot be tolerated in the less efficiently ventilated engine spaces of marine craft.
Additionally, within marine craft, the engine and muffler are often mounted amidship and located as far as 30 ft. to 40 ft. (9 m. to 12 m.) from the exhaust terminus. At these lengths, it is difficult to maintain an overall downward grade necessary to drain the waste coolant water separated from the exhaust flow solely by means of gravity. In practice, the exhaust conduit leading from the muffler to the exhaust terminus may curl up-and-down as it crosses various sections of the marine craft, creating traps where water may accumulate and constrict the exhaust gas flow.
Consequently, there remains a need for a reliable and effective marine wet exhaust system capable of attenuating exhaust noise and capable of separating waste cooling water from the exhaust gases before the waste cooling water and dewatered exhaust gases are discharged into the environment. There is an even more specific need for such a system that is also capable of separating and retaining particulates and other petroleum based contaminants from the waste cooling water and the dewatered exhaust gas before discharging either into the environment.
These needs and others are addressed, in accordance with the invention, by means of a preferred marine wet exhaust system including a separator and a particulate capture and containment system. The preferred separator receives an exhaust gas and waste cooling water mixture with entrained particulates and other petroleum based contaminants. It functions to separate at least a portion of the waste cooling water with the entrained particulates from the exhaust gas. A first preferred particulate capture and containment system includes a reservoir interposed between the separator and the filter. The filter receives the waste cooling water with the entrained particulates and serves to separate most of the particulates from the waste cooling water. The reservoir serves as a buffer to allow the flow rate through the filter to differ from the flow rate through the water supply pump.
In accordance with an especially preferred embodiment, a reservoir discharge pump is interposed between the reservoir and the filter to control the water level in the reservoir. According to one form of the invention, the reservoir discharge pump is switched ON and OFF by means of a suitable level sensor, such as a level sensing tube, communicating with the interior of the reservoir. The preferred level sensor detects minimum and maximum desired water levels in the reservoir and selectively activates the reservoir discharge pump so as to maintain the water level within a neighborhood of those bounds. According to another form of the invention, the reservoir discharge pump is a variable rate pump operating in response to a controller so as to match the rate of the variable rate reservoir discharge pump to the rate at which the cooling water supply pump is drawing water into the preferred marine wet exhaust system. One advantage of the use of a variable speed pump is that it allows the capacity of the reservoir to be reduced in comparison with the capacity otherwise required; indeed, it is within the contemplation fo the invention to replace the reservoir with a suitable variable speed pump.
It is well known that the life of a pump driven by an electrically powered motor is affected significantly by the number of ON and OFF duty cycles to which the motor is subjected. An improvement to the marine wet exhaust system in accordance with the present invention, incorporates a pressure transducer connected to a level sensing tube appropriately positioned in the reservoir. The output of the transducer is transmitted to a variable flow rate controller. This controller, in turn, varies the speed of an electric motor driving the reservoir discharge pump. The level of water in the reservoir can thus be maintained within closer limits than with use of an ON/OFF switching means alone. Running the reservoir discharge pump motor continually, with automatic speed variations, tends to improve the life of the electric motor.
In accordance with another especially preferred embodiment, the marine wet exhaust system includes a reservoir drain line communicating between the reservoir and an exterior of the craft. Even more preferably, the reservoir is sealed in a confined space isolated from other interior spaces of the craft. In the event that the reservoir discharge pump fails and automatic control of the water level in the reservoir is lost, there is a risk that excess water will flood the interior spaces and adversely affect the operation of the craft. In such an event, the confined space serves to contain the excess water and the reservoir drain line provides a flow path for conducting such excess water overboard. Additionally, during normal operation, the reservoir drain line provides a flow path for discharging exhaust gases, if any, which fail to separate from the waste cooling water in the separator.
In accordance with yet another especially preferred embodiment, the marine wet exhaust system includes a bleed line, most preferably a small gauge bleed line, communicating between the upper portion of the interior of the filter housing and the reservoir. It has been found that the effectiveness, and therefore the useful life, of the filter elements within the filter housing are maximized by providing a means for keeping the filter elements completely submerged in water at all times. Due to minor leaks in the system piping, or more often by the inclusion of air or other gases in the water that is being pumped from the reservoir to the filter housing, air or other gases can accumulate in the upper portions of the filter housing. These accumulated gases displace water that normally would cover the extremities of the filter element. The bleed line provides a vent through which the entrapped air or other gases can escape to the reservoir, which, in turn, communicates to atmosphere, thereby maximizing the effectiveness and useful life of the filter element.
Another improvement to the marine wet exhaust system is the use of a filter element infused with an organic coagulant medium such as MYCELX(copyright) filter compound, available from Mycelx Technologies Corporation of Gainesville, Ga. The filter cartridge, so infused, has the capability of absorbing very high amounts of diesel and gasoline range organic materials. The effluent from the filter likely will contain less than one part per million of these petroleum based contaminants. There is minimal increase in the pressure differential across the filter as the contaminant level absorbed by the filter increases, as is the case in many other filters or filter media used in similar applications. This results in negligible decrease in the flow rate as the filter element approaches saturation with removed contaminants.
A second preferred particulate capture and containment system includes an exhaust gas conduit communicating with the separator and a condensate trap located within, or near, a terminus of the exhaust gas conduit. The preferred condensate trap includes a housing defining first and second chambers. The first chamber defines spaced inlet and outlet lines. A condensate trap drain line communicates with the second chamber. A plurality of passageways, most preferably defined by slots or other appropriately configured openings of various configurations, communicate between the first and second chambers. Most preferably, the first chamber is substantially cylindrical; the condensate trap is positioned such that an axis defined by the first chamber lies no more than 45xc2x0 from horizontal; and the passageways are downwardly directed, so as to induce relatively dense fluids and particulates to pass from the first chamber to the second chamber through the passageways under the influence of gravity.
The condensate trap serves to separate particulates and condensates from the de-watered exhaust gases discharging through the exhaust conduit. The de-watered exhaust gases which flow from the inlet line to the outlet line through the first chamber of the condensate trap are rich in condensed diesel or other fuel used in the engine as well as entrained particulates. Rather than emit these particulates and other condensates to the environment, the condensates and particulates are induced to pass from the first chamber to the second chamber through the passageways. The liquid and particulates accumulate in the second chamber and ultimately exit through the condensate trap drain line to the reservoir, so as to either settle in the reservoir or be captured in the filter.
Therefore, it is one object of the invention to provide a reliable and effective marine wet exhaust system capable of attenuating exhaust noise. It is another object of the invention to provide a marine wet exhaust system capable of separating particulates and other contaminants from exhaust gases and waste cooling water before the de-watered exhaust gases and the waste cooling water are discharged into the environment. In accordance with the first preferred embodiment, this is accomplished by separating the waste cooling water and entrained particles from the exhaust gas in the separator; accumulating the waste cooling water and entrained particulates in the reservoir; and separating the entrained particulates from the waste cooling water in the filter. Means including the reservoir discharge pump, the reservoir drain line and the bleed line serve to control the water levels in the reservoir and the filter so as to improve the operation of the marine wet exhaust system. In accordance with the second embodiment, the condensate trap separates particulates and condensates from the de-watered exhaust gas, most preferably returning the particulates and condensates to the reservoir and then to the filter where they will be entrapped.
The present invention will be further described in the appended drawings, following detailed description and the appended claims.